1. Two wattmeters are used to measure the power in a 3-phase balanced system. What is the power factor of the load when one wattmeter reads twice the other?

2. Two wattmeter method is used for the measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other (both positive), then the power factor of the load is

3. A wattmeter is connected as shown in the figure. The wattmeter reads

Zero always

Total power consumed by Z1 and Z2

Power consumed by Z1

Power consumed by Z2

Answer.4. Power consumed by Z2

Explanation:

Wattmeter reads the power and it is given by

P = V_{PC }I_{CC }cos ϕ

V_{PC} is the voltage across the pressure coil

I_{CC} is current flows through the current coil

ϕ is the phase angle between V_{PC} and I_{CC}

Application:

The circuit representation of the given question is as shown below.

The potential coil is connected across Z_{2}.

It reads the voltage across Z_{2} only.

So, Wattmeter reads only power consumed by Z_{2}.

5. In a two-wattmeter method of measuring power in a balanced 3-phase circuit, the ratio of the two-wattmeter reading is 1:2. The circuit power factor is

6. In the measurement of the power of balanced load by two wattmeter method in a 3-phase circuit, The readings of the wattmeters are 4 kW and 2 kW respectively, the latter is being taken after reversing the connections of the current coil. the power factor and reactive power of the load is

0.2 & 6 kVAR

0.2 & 6 √3 kVAR

0.32 & 2 kVAR

0.32 & 2 √3 kVAR

Answer.2. 0.2 & 6 √3 kVAR

Explanation:

Given that,

Reversing the connections

W1 = 4 kW, W2 = – 2 kW

Total reactive power (Q) = √3[4 – (- 2)] = 6 √3 kVAR

7. In a balanced 3-phase 200 V circuit, the line current is 115.5 A. When the power is measured by two wattmeter methods, one of the wattmeters reads 20 kW and the other one reads zero. What is the power factor of the load?